An iPhone 7 is still perfectly usable, in my experience. They also should still be supported for a while. Used, they can easily be found around the $200 price point.
Can confirm, on a 7 Plus, phone's entirely fine, no problems at all. I don't expect to replace it for another two years or so, unless it breaks. Probably by the end of that it'll be feeling a little slow and the battery'll be down to 36hrs rather than lasting all weekend.
Also on a used first-gen iPad Pro 12.9". It's great. I may sell it and pick up a used 3rd-gen when the 4th gen comes out. Or may wait one past that, pick up a used 4th, and just give the 1st-gen to my kids rather than selling. Apple devices are worth the money in part because they don't go way downhill after 12-18mo, so 1) they actually hold some value, and 2) you can skip a couple upgrades and not feel like you're missing out on much.
